/*
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
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 */
package java.util.stream;

import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Objects;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.IntFunction;

/**
 * Factory methods for transforming streams into duplicate-free streams, using
 * {@link Object#equals(Object)} to determine equality.
 *
 * @since 1.8
 */
final class DistinctOps {

  private DistinctOps() {
  }

  /**
   * Appends a "distinct" operation to the provided stream, and returns the
   * new stream.
   *
   * @param <T> the type of both input and output elements
   * @param upstream a reference stream with element type T
   * @return the new stream
   */
  static <T> ReferencePipeline<T, T> makeRef(AbstractPipeline<?, T, ?> upstream) {
    return new ReferencePipeline.StatefulOp<T, T>(upstream, StreamShape.REFERENCE,
        StreamOpFlag.IS_DISTINCT | StreamOpFlag.NOT_SIZED) {

      <P_IN> Node<T> reduce(PipelineHelper<T> helper, Spliterator<P_IN> spliterator) {
        // If the stream is SORTED then it should also be ORDERED so the following will also
        // preserve the sort order
        TerminalOp<T, LinkedHashSet<T>> reduceOp
            = ReduceOps.<T, LinkedHashSet<T>>makeRef(LinkedHashSet::new, LinkedHashSet::add,
            LinkedHashSet::addAll);
        return Nodes.node(reduceOp.evaluateParallel(helper, spliterator));
      }

      @Override
      <P_IN> Node<T> opEvaluateParallel(PipelineHelper<T> helper,
          Spliterator<P_IN> spliterator,
          IntFunction<T[]> generator) {
        if (StreamOpFlag.DISTINCT.isKnown(helper.getStreamAndOpFlags())) {
          // No-op
          return helper.evaluate(spliterator, false, generator);
        } else if (StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
          return reduce(helper, spliterator);
        } else {
          // Holder of null state since ConcurrentHashMap does not support null values
          AtomicBoolean seenNull = new AtomicBoolean(false);
          ConcurrentHashMap<T, Boolean> map = new ConcurrentHashMap<>();
          TerminalOp<T, Void> forEachOp = ForEachOps.makeRef(t -> {
            if (t == null) {
              seenNull.set(true);
            } else {
              map.putIfAbsent(t, Boolean.TRUE);
            }
          }, false);
          forEachOp.evaluateParallel(helper, spliterator);

          // If null has been seen then copy the key set into a HashSet that supports null values
          // and add null
          Set<T> keys = map.keySet();
          if (seenNull.get()) {
            // TODO Implement a more efficient set-union view, rather than copying
            keys = new HashSet<>(keys);
            keys.add(null);
          }
          return Nodes.node(keys);
        }
      }

      @Override
      <P_IN> Spliterator<T> opEvaluateParallelLazy(PipelineHelper<T> helper,
          Spliterator<P_IN> spliterator) {
        if (StreamOpFlag.DISTINCT.isKnown(helper.getStreamAndOpFlags())) {
          // No-op
          return helper.wrapSpliterator(spliterator);
        } else if (StreamOpFlag.ORDERED.isKnown(helper.getStreamAndOpFlags())) {
          // Not lazy, barrier required to preserve order
          return reduce(helper, spliterator).spliterator();
        } else {
          // Lazy
          return new StreamSpliterators.DistinctSpliterator<>(helper.wrapSpliterator(spliterator));
        }
      }

      @Override
      Sink<T> opWrapSink(int flags, Sink<T> sink) {
        Objects.requireNonNull(sink);

        if (StreamOpFlag.DISTINCT.isKnown(flags)) {
          return sink;
        } else if (StreamOpFlag.SORTED.isKnown(flags)) {
          return new Sink.ChainedReference<T, T>(sink) {
            boolean seenNull;
            T lastSeen;

            @Override
            public void begin(long size) {
              seenNull = false;
              lastSeen = null;
              downstream.begin(-1);
            }

            @Override
            public void end() {
              seenNull = false;
              lastSeen = null;
              downstream.end();
            }

            @Override
            public void accept(T t) {
              if (t == null) {
                if (!seenNull) {
                  seenNull = true;
                  downstream.accept(lastSeen = null);
                }
              } else if (lastSeen == null || !t.equals(lastSeen)) {
                downstream.accept(lastSeen = t);
              }
            }
          };
        } else {
          return new Sink.ChainedReference<T, T>(sink) {
            Set<T> seen;

            @Override
            public void begin(long size) {
              seen = new HashSet<>();
              downstream.begin(-1);
            }

            @Override
            public void end() {
              seen = null;
              downstream.end();
            }

            @Override
            public void accept(T t) {
              if (!seen.contains(t)) {
                seen.add(t);
                downstream.accept(t);
              }
            }
          };
        }
      }
    };
  }
}
